This invention relates to a system for the cooling of structures or other enclosures. It is especially suitable for situations where cooling requirements, or the "load", may vary substantially. It is therefore particularly useful for the air-conditioning of building structures.
The minimization of requirements for operating cooling systems of all kinds has become increasingly important with the recent rise in related costs. One means for doing so would be to overcome the drawbacks of cycles inherent in the operation of these systems. Unfortunately, these means are not readily available.
There are two main cycles that have contributed to these costs. First, cooling requirements are sporadic. To meet them, it has been necessary to provide refrigeration or chiller equipment having a capacity substantially over average cooling requirements. Thus excess capital investment has been needed to meet peak load requirements. Second, power costs fluctuate with general demand and cooling requirements ordinarily parallel that demand. As a consequence, maximum rates are generally paid for power utilized in cooling.
The present invention seeks to overcome these prior art problems through an integrated system involving build-up of an efficient, reserve cooling capacity. This capacity may be generated during low-load periods of time at which power costs are minimal. Through this system, smaller and less costly refrigeration equipment can also be employed to meet even peak cooling load requirements.
These objectives may be achieved utilizing equipment primarily derived from conventional cooling systems. Such systems normally include three zones. These are: a cooling zone; a refrigeration zone; and a heat collection (or dissipation) zone.
The cooling zone is normally essentially co-extensive with the boundaries of the enclosure to be cooled. Thus, for example, in an office building, it would generally encompass the entire work space.
This zone should contain a conduit (or conduits) for conveying a cooling fluid and means for propelling the fluid through the conduit(s) to where the load occurs. Many such embodiments are readily apparent. Most buildings, for example, utilize forced air blown through conduits into individual rooms. In other situations, such as a freezer, recirculating fluids may be pumped through walls, or pipes in walls, surrounding the materials to be cooled. All these forms are compatible with the present invention.
The heat collection or dissipation zone is normally quite separate from the cooling zone. It is utilized to remove energy extracted from refrigerant by the chiller means in the refrigeration zone. All that is required for this zone is a collection means, many of which are again conventional. They may, for example, simply constitute an air cooled condenser, a standard building cooling tower or other heat rejection devices. For conservation of energy, it is preferred that the zone be one which transfers the energy to another use. Thus it may include a commercial converter means utilized for concentrating energy and producing, for example, hot water for the building.
Between the heat collection (or dissipation) means and the cooling zone is the refrigeration zone. In overall perspective, it functions to extract energy from the cooling fluid while exhausting energy to the collection means. The present refrigeration zone, like many conventional ones, should contain a closed refrigeration circuit, means for circulating refrigerant therein and chiller means within the circuit for removal of energy from the refrigerant.
In addition, the refrigeration zone of this invention contains a storage reservoir within the circuit. This reservoir is desirably large enough to hold a substantial amount ice/water mixture, preferably over 50% of the average daily cooling zone requirements and most preferably over 70%. The reservoir is generally thermally insulated and, in the case of use for air-conditioning buildings or the like where it may be very large and heavy, is located securely, as in the basement.
In accordance with the present invention, the refrigerant is unusual. It is composed of a slurry of ice and water. Where desired, it may additionally contain a freezing point depressant such as glycol (generally from about 5 to 25% by volume), salt (such as NaCl, CaCl.sub.2, KF or Na.sub.2 SO.sub.4) or the like. This permits the refrigerant to remain fluid at lower temperatures and so increases the cooling capacity of the system.
The refrigeration zone may actually be composed of two or more sub-circuits. Most efficient operation results where there is a sub-circuit including the chiller means and another connectable to the cooling zone. These sub-circuits must overlap partially and most commonly through mutual access to the storage reservoir, or reservoirs, should more than one be desired. Slurry may be shifted therebetween by conventional valves, pumps and conduits.
When in the storage phase of operation, a reserve cooling capacity is generated in this zone both by reducing the temperature of the refrigerant and by freezing water to ice. This is accomplished by passing the refrigerant through the chiller means as often as necessary. The slurry may then be recycled to the storage reservoir where, preferably while being maintained in motion by, for example, pumping it through small piping or by mechanical agitation, substantial pockets of complete solidification are avoided.
The amount of ice in the storage reservoir varies cyclically. During the storage phase where more and more water is frozen by passing slurry through the chiller, however, it approaches 70% by volume of the slurry. It may at other times fall to none, although normally the amount ranges between 10 and 70%, preferably 20 to 70%.
This storage phase of operation is performed primarily at times of minimim load requirement and lowest power cost. Both times generally coincide with night or other non-work periods. As a result, there is ample opportunity in which slowly to store a reserve cooling capacity (thereby reducing the capacity requirement for the chiller means) while saving on power.
When load requirements increase--normally during day time and working hours--and operation shifts to the cooling phase, it may not even be necessary to power the chiller means. Except under a very high load, there will be sufficient capacity stored to provide cooling throughout the day. This is not to say, however, that the chiller cannot be operated to yield auxillary cooling during peak load periods in conjunction with reliance upon the stored capacity.
During the cooling phase, the slurry is cycled to permit connection with the cooling zone. This is easily accomplished by simultaneously passing the cooling fluid and water from the slurry through, for example, a conventional heat exchanger means. There, an additional facet of the present invention becomes apparent. Because of the presence of ice in the slurry, the refrigerant itself possesses an especially high latent cooling capacity and can relay that reserve indirectly to the cooling fluid.
The novel features of the invention, as well as additional objects and advantages thereof, will be understood more fully from the following description when read in conjunction with the accompaning drawing.